In disk-type magnetic recording systems for digital applications, magnetic transducer elements, or heads, are used to record information onto (i.e., write) or retrieve information from (i.e., read) the disk surface or surfaces. Each storage disk comprises an annular substrate onto which is deposited a magnetic recording medium. Each disk surface is divided into thousands of concentric, annular bands, or "tracks" each having a predetermined radial extent. Each head is supported in close proximity to an associated disk surface by a head positioning assembly, or actuator, that supports the head near the disk surface and moves it from one radial position to another, thereby permitting use of a single head for reading and writing along multiple concentric tracks. The positioner assembly for each head or group of heads includes an actuator arm and an actuator motor. The actuator motor moves the actuator arm, to change the position of the head with relation to the tracks on the disk. A disk drive may include a plurality of stacked disks, and one actuator motor may be used to move a corresponding number of actuator arms in unison.
Positioner assemblies of the prior art typically consist of several arms, in spaced apart relationship, stacked one above the other, pivoted at their centers on a common pivot, with read/write heads mounted at one end and the moving winding of the rotor of the actuator motor mounted at the other. The stator portion of the motor includes permanent magnets for the actuator motor as well as a flux return path that is typically formed of steel. The winding acts as a magnetic field generator as well as a counterweight to balance the heads and the actuator arms.
During operation, the positioner assembly provides high speed disk file access by positioning the read/write heads in a transducing relationship with a rotating magnetic storage disk. Such operation requires, first, that the position of the read/write head relative to a track on the disk be maintained within extremely close tolerances; and, second, that the access time (that is, the time required to move the head from one track to another desired track) be short. The state of the art concerning the first requirement necessitates that a control system, preferably utilizing feedback, be employed to sense the deviation of the position of the head from an optimum read/write position over the track, and to generate a correction signal for driving the actuator motor. A short access time, on the other hand, requires a number of different considerations such as the voice coil motor design, the moving mass, and inertia of the positioner and heads. Additionally, access time depends on the actuator assembly's structural design as well as the servo control algorithm employed for controlling the positioning of the actuator assembly.
One alternative for minimizing disk file access time is to increase the torque of the actuator motor for increasing the acceleration and deceleration of the positioner assembly. However, in order to increase the torque of an actuator motor, a proportional increase in overall motor size is required. Another alternative for increasing the acceleration and deceleration of the positioner assembly is to increase the magnitude of the current profiles supplied to the actuator motor windings. Both of the above described methods increase the acceleration and deceleration of the positioner assembly, however, both method cause an undesirable increase in power consumption.
Thus, a hitherto unsolved need has remained for an actuator motor that reduces average access time to a disk file storage system with no increase in power consumption and motor size.